Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve the use of a balloon catheter with a guide wire, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached proximate the proximal end. In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
There are two basic types of balloon catheters used in combination with a guide wire, namely, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The construction and use of both standard OTW catheters and standard SOE catheters are well-known in the art. An example of an OTW catheter may be found in commonly-assigned U.S. Pat. No. 5,047,045 to Arney et al. An example of an SOE balloon catheter is disclosed in commonly-assigned U.S. Pat. No. 5,156,594 to Keith.
PTA and PTCA catheters are preferably designed to optimize pushability, trackability and crossability. Pushability is defined as the ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability is defined as the ability to navigate tortuous vasculature. Crossability is defined as the ability to navigate the balloon catheter across narrow restrictions or obstructions in the vasculature.
One type of OTW balloon catheter is a coaxial OTW balloon catheter. A coaxial OTW catheter typically includes two separate tubes, namely an inner tube and a coaxially disposed outer tube. The inner tube defines a guide wire lumen and an annular inflation lumen is defined between the inner tube and the coaxially disposed outer tube. In a standard OTW coaxial catheter, the outer tube has a proximal end which is fixed to a manifold with the lumen of the outer tube in fluid communication with a side port in the manifold for injection of inflation fluid. The outer tube extends distally to the proximal waist of an inflatable balloon, with the proximal waist of the balloon secured to the distal portion of the outer tubular member. The lumen of the outer tubular member is in fluid communication with the internal volume of the balloon. The inner tubular member also includes a proximal end which terminates in the manifold, however, the inner tubular member terminates at a point proximal to the termination of the outer tubular member with the lumen of the inner tube extending straight through the manifold to a port which is axially aligned with the lumen so that a guide wire may be extended therethrough. The side port of the manifold for inflation is thus only in fluid communication with the annular space formed between the tubes. The inner tubular member extends distally to a point beyond the distal termination of the outer tubular member with the inflatable balloon extending from proximate the distal end of the outer tubular member to a point proximate the distal end of the inner tubular member onto which it is adhered. The manifold attachment of the inner and outer tubular members secures these tubular members relative to each other.
Prior art coaxial OTW-type balloon catheters have attempted to maximize pushability by incorporating a stainless steel outer tube on the proximal shaft portion (also referred to as a hypotube) and a polymeric distal shaft portion. Hypotubing is, however, prone to kinking. Coaxial OTW-type balloon catheters can also incorporate a polymer shaft or a reinforced polymer shaft as a proximal shaft portion (e.g. composite) with recognized loss of pushability as a compromise between maximizing pushability and minimizing the probability of kinking in the proximal shaft portion.
The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter, as this portion must track the guidewire through small tortuous vessels to reach the stenosed area to be treated. A more flexible distal portion has been found to improve trackability. Further, in transitioning from a stiff proximal segment or portion of the catheter shaft to a more flexible distal portion of the catheter shaft, it has been found that kinking readily occurs at the joint between the two shaft segments of differing flexibility. The increased flexibility of the distal section also makes this portion of the catheter less able to be pushed from the proximal end of the catheter.
Even with the prior art emphasis on improved pushability, trackability and crossability, it has still been found that there are many stenotic lesions or restrictions in blood vessels through which present OTW catheters cannot be passed. In some of these restricted vessel regions, it is possible to pass the guide wire distal portion through the restriction, yet it is found that the balloon angioplasty catheter itself cannot cross the restriction to place the balloon for expansion. This has also been found to be true when metallic stents, which are presently utilized for permanently holding a blockage open, are already within the blood vessel lumen through which a catheter must be tracked. The stent itself includes struts of wire having interstitial spaces between such struts into which the catheter distal tip can become lodged and caught. This can prevent further advancement through the stent lumen.
Many times the problems associated with crossing the placed stent or, in the alternative, crossing a tight vascular restriction present within the vessel, are compounded by the tortuous path that the lumen of the vessel follows at that point. In particular, it has been found to be difficult to pass the catheter through a highly restricted bend or through a stent which is placed within a bend in the vessel. There is, therefore, a need for a balloon dilatation catheter which incorporates features for improving the ability of the catheter to cross a tight vascular restriction or otherwise blocked region of the vessel through which a guide wire has already been placed. Further, there is a need for a balloon dilatation catheter having improved capability for passing through the lumen formed by a stent placed within the vessel, which would otherwise cause present distal tips on catheters to catch on or lodge against the stent struts.